1. Field of the Invention
The present invention relates generally to user input devices, and in particular, to a transmitter and receiver for use in a wireless cursor pointing system.
2. Background Art
Initially, input devices such as mice and track-balls were all tethered to a personal computer (PC) via a cable or wire. Because of the inconvenience and inflexibility of wired input devices, there was a need for an effective wireless mouse.
One type of conventional wireless mouse employed infra-red transmission and detection. However, because of the line-of-sight restrictions for infra-red transmissions, this approach was not successful. Another conventional wireless mouse employed amplitude modulation (AM) schemes. However, because AM modulated signals are subject to interference from many sources (e.g., radios, monitors employed in a computer system, and other appliances), this approach was also ineffective.
Conventional wireless mice do not currently employ frequency modulation (FM) schemes. One benefit of FM is that it can provide better discrimination against noise and interference than AM. However, conventional FM systems in cordless phones or similar wireless devices (i.e., an interphone) for analog transmission generate an FM wave with frequency deviation using the modulation method of the variable capacitance diode, but their associated circuits are complex and costly to implement.
Furthermore, receivers employed in conventional wireless mouse systems are designed to improve the sensitivity (i.e., ability to receive weaker signals) of the receivers, and to improve the selectivity (i.e., ability to separate the signals of different stations) of the receivers. As a result, the circuits for these receivers can be complex and costly. In addition, conventional receivers have three types of output circuits or buffers, as shown in FIGS. 8A-8C. For example, FIG. 8A illustrates an output circuit that provides reverse output through a combination of transistors and load resistance, thereby increasing current and power dissipation of the circuit. The buffer in FIG. 8B is a differential amplifier, which can increase cost and waste power. The buffer in FIG. 8C employs a three transistor exchange output circuit which requires a push-pull amplifier. The buffer in FIG. 8C adds to the complexity and the cost of the receiver.
Accordingly, there remains a need for a wireless cursor pointing system that includes a transmitter and a receiver that overcome the disadvantages set forth previously in a cost-effective manner while maintaining good signal quality.
It is an object of the present invention to provide a wireless cursor control system having a high frequency transmitter circuit disposed in the cursor pointing device.
It is another object of the present invention to provide a wireless cursor control system having a high frequency transmitter circuit with a high frequency circuit for increasing the frequency deviation of the oscillation frequency.
It is a further object of the present invention to provide a wireless cursor control system having a high frequency transmitter circuit with a variable frequency modulation circuit for selectively changing the amount of frequency deviation of the variable frequency.
It is also an object of the present invention to provide a wireless cursor control system having a high frequency receiver with a double transistor exchange output having low current consumption, thereby reducing loading effect.
The objects of the present invention can be accomplished by providing a wireless cursor control system that includes a pointing device and a receiver. The pointing device has a controller for receiving user input and for providing a control signal, and a transmitter that includes an antenna and a high frequency modulator coupled to the controller for receiving the control signal and for generating an output signal for transmission via the antenna. The high frequency modulator includes a variable frequency modulator circuit for selectively changing the frequency deviation of the control signal, and a high frequency circuit for increasing the frequency deviation of the control signal to produce the output signal. The receiver has an antenna that receives the output signal, and a demodulation circuit for demodulating the received output signal.